Journal Article

On the use of phloem sap <i>δ</i><sup>13</sup>C as an indicator of canopy carbon discrimination

Katherine G. Rascher, Cristina Máguas and Christiane Werner

Edited by James Ehleringer

in Tree Physiology

Volume 30, issue 12, pages 1499-1514
Published in print December 2010 | ISSN: 0829-318X
Published online November 2010 | e-ISSN: 1758-4469 | DOI:
On the use of phloem sap δ13C as an indicator of canopy carbon discrimination

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In this study we measured δ13C in various carbon pools along the basipetal transport pathway in co-occurring Pinus pinaster and Acacia longifolia trees under Mediterranean climate conditions in the field. Overall, species differences in photosynthetic discrimination resulted in more enriched δ13C values in the water-conserving overstory P. pinaster relative to the water-spending understory invasive A. longifolia. Post-photosynthetic fractionation effects resulted in differences in δ13C of water-soluble organic matter pools along the plant axis with progressive depletion in δ13C from the canopy to the trunk (∼6.5‰ depletion in A. longifolia and ∼0.8‰ depletion in P. pinaster). Regardless of these fractionation effects, phloem sap δ13C in both terminal branches and the main stem correlated well with environmental parameters driving photosynthesis for both species, indicating that phloem sap δ13C has potential as an integrative tracer of changes in canopy carbon discrimination (Δ13C). Furthermore, we illustrate that a simple model based on sap flow estimated canopy stomatal conductance (GS) and phloem sap δ13C measurements has significant potential as a tool for estimating canopy-level carbon assimilation rates.

Keywords: canopy photosynthesis; carbon isotope discrimination; carbon transport; stable isotope fractionation; respired CO2

Journal Article.  10032 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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